N908DKPiper PA-32-300 · 1973

On May 8, 2024, about 1130 eastern daylight time, a Piper PA-32-300, N908DK, was substantially damaged when it was involved in an accident near Apopka, Florida. The company pilot and -pilot/owner were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight.

The airplane sustained a loss of engine power on April 4, 2023. Maintenance was performed over the next 10 months and an annual inspection was completed on February 13, 2024.

On the day of the accident, a pilot employed by the company that performed the maintenance flew the airplane (company pilot) from Bartow Executive Airport (BOW), Bartow, Florida, to Orlando Executive Airport (ORL), Orlando, Florida, where he picked up the pilot/owner. The flight was uneventful. The pilots intended to return to BOW, where the pilot/owner would pay his bill before flying the airplane back to the airport where it was based. After departure, the pilots initiated a climb to 2,500 ft msl, during which the engine began to run “rough.” The company pilot noticed that two cylinders had stopped producing power and asked the pilot/owner to look up the common traffic advisory frequency for the closest airport, which he did. An emergency radio transmission was made and the pilot/owner noticed that two more cylinders had stopped producing power and the airplane was unable to maintain altitude. The company pilot performed a forced landing, during which the left wing struck a tree and sustained substantial damage.

Postaccident examination of the wreckage by a Federal Aviation Administration inspector found fuel in all wing fuel tanks. Compression was observed on all cylinders, and the engine was visually inspected with no preaccident anomalies noted. The engine was subsequently sent to the manufacturer’s factory for continued examination and a test run.

Before the test run, data that included engine data parameters were extracted from the onboard avionics. The data showed that, 5 minutes and 15 seconds after rotation, at 1125:00, the exhaust gas temperature (EGT) on the No. 2 cylinder began to reduce. At 1126:34, the No. 4 cylinder EGT began to drop, followed by the No. 3 cylinder EGT at 1126:45. The No. 6 cylinder EGT began to fluctuate up and down at 1127:38, before eventually dropping at 1129:20. At 1129:13, the engine rpm began to reduce from 2,380 and continued to drop until impact. The data also showed that the oil temperature during the flight reached a maximum of 231° F. As the EGT in the cylinders dropped, the cylinder head temperatures (CHT) also began to drop.

A test run was performed at the manufacturer’s factory. During the test run, the engine was started and warmed up with the oil temperature reaching approximately 250° F by the time the engine was about 2,000 rpm. The engine was shut down and the oil filter adapter, with the thermostatic oil cooler bypass valve (vernatherm), was removed and a substitute oil filter adapter was installed. The engine run was completed with the engine operating through its full power band following the manufacturer’s standard power and leak engine run test. All areas passed except for the air flow limits at rated power. The low limit was 1,636.6 pounds per hour (pph); the test result was 1,535.3 pph. The manufacturer reported that the airflow number would equate to the engine being slightly low on power but was not low enough that they would expect a pilot to be able to discern a difference during normal operation of the airplane. Visual examination of the original oil filter adapter and the thermostatic oil cooler bypass valve revealed a witness mark of the valve that was not uniform, consistent with the valve not seating properly. An improperly seated valve would allow hot oil to partially bypass the oil cooler, resulting in excess oil temperatures consistent with those found when the engine was run on the test stand with the original oil filter adapter.

A subsequent examination of the airplane was conducted with the airframe manufacturer. The examination found no preaccident obstructions or leaks in the fuel system. The fuel selector remained installed in the airframe. Air was applied through the fuel system, confirming appropriate flow in all fuel selector positions. Each fuel selector position exhibited a tactile detent. The fuel selector valve/fuel strainer screen was unobstructed. The fuel boost pump was tested and ran smoothly when external power was applied. The fuel flow transducer remained attached to the airframe and was removed and checked for blockages. The transducer was unobstructed and the fuel flow measuring wheel rotated normally.

The spark plugs were removed and the electrode wear appeared normal. The spark plug electrodes were visibly darker than normal, consistent with an excessively rich fuel to air ratio. The exhaust valve springs were dark in color and were intact on all cylinders. The exhaust valve stem of cylinder No. 1 appeared clean, with no buildup or residue noted. The exhaust valve stems for cylinder Nos. 2, 3, 4, 5, and 6 had moderate buildup of carbon at the combustion chamber side of the exhaust guide. The exhaust valve stem of cylinder No. 4 caught and was tight when it was pushed into the cylinder head.

The pilot/owner reported that in March 2023 the airplane had “lost” a cylinder in flight and an emergency landing was performed to a local airport. He contacted his maintenance provider, who reported to him over the phone that it was likely bad fuel or an improper mixture setting. He also reported that in April 2023 the airplane again exhibited cylinders shutting down in flight; again, an emergency landing was performed to a local airport. A maintenance work order indicated that the maintenance facility installed a new starter and cleaned the No. 6 cylinder nozzle and spark plugs, and then the airplane was put back into service. In May 2023 the airplane again exhibited cylinders shutting down in flight and the pilot was forced to make an emergency landing on a roadway. The airplane was recovered and taken to the maintenance facility. The work order for the work performed after this incident stated, in part, “reassembled aircraft after engine quit due to bad cylinder.”

Personnel at the maintenance facility were asked if, during their troubleshooting of the engine, they reviewed the available data from the engine monitoring device (EMD). Their initial response was “…no. He had just put in a Garmin 1000 and there was no engine monitoring system when we did the last annual.” The avionics had been installed in February 2022, and since that time the maintenance shop had completed two annual inspections and an examination after a reported engine issue. The maintenance personnel further stated, “We don't normally look at engine monitoring, if we do, the customer has provided it to us.”

A review of historical data recovered from the EMD revealed similar cylinder EGT drops on multiple other flights. These flights coincided with the other engine malfunctions the pilot/owner reported. The historical data also revealed the airplane oil temperature had exceeded 220° F multiple times since August 2022, with a maximum recorded oil temperature of 247° F. The Lycoming Operator’s Manual stated, “The maximum permissible oil temperature is 245°F (118°C). For maximum engine life, desired oil temperature should be maintained between 165°F (73.8°C) and 200°F (93.3°C) in level flight cruise conditions.”

A review of maintenance logbooks showed that the engine was last overhauled on November 1, 1997. From the annual inspection in 2018 to the annual inspection in 2024, the airplane had accumulated 84 hours. The most recent annual inspection was completed on February 13, 2024. During this annual inspection, the No. 1 cylinder was replaced. The logbook entry stated the No. 2 cylinder had been replaced but the shop reported that this was a “typo” and it was, in fact, the No. 1 cylinder that was replaced. No other cylinder replacements were noted since the engine had been overhauled in 1997. There were no maintenance logbook entries that indicated compliance with Lycoming Service Bulletin 388 (described below).

Further, there was no evidence of the exhaust guides being replaced with the “improved material” guides described in Lycoming Service Instruction 1485 (below).

Lycoming Service Instruction 1009 stated, in part, “All engine models are to be overhauled within twelve (12) calendar years of the date they first entered service or of last overhaul. This calendar year time period TBO is to mitigate engine deterioration that occurs with age, including corrosion of metallic components and degradation of non-metallic components such as gaskets, seals, flexible hoses and fuel pump diaphragms.”

Lycoming Service Instruction 1425 stated, in part, “Field experience has shown that engine oil contamination increases the possibility of sticking and/or stuck valves. This situation occurs when the contaminants in the engine lubrication oil become deposited on the valve stems, restricting the valve movement, and resulting in intermittent engine hesitation or miss. If corrective action is not taken to remove the deposits, a valve could become stuck causing engine damage. Since the rate of oil contaminant accumulation is increased by high ambient temperatures, slow flight with reduced cooling, and high lead content of fuel, owners and operators experiencing these conditions are encouraged to consider the following suggestions for operation and maintenance if they have experienced valve sticking.”

Lycoming Service Instruction 1485 stated, in part, “Once guides made from the improved material are installed in all cylinders on the engine, it is no longer necessary to complete the mandatory 400 hour inspections specified in the latest revision of Service Bulletin No. 388. It is recommended that the inspection procedure from the latest revision of Service Bulletin No. 388 be completed at 1000 hours of operation or half way to the recommended TBO, whichever occurs first. (For recommended TBO, refer to the latest revision of Service Instruction No. 1009.)”

Improved exhaust valve guides were initially incorporated into some cylinder assemblies beginning in April 1996. Since March 1, 1998, all engines, cylinder kits and spare exhaust valve guides shipped from Lycoming contain the improved material.

From Lycoming Service Bulletin 388:

Time of Compliance:

Helicopter Engines–300 hour intervals or earlier if valve sticking suspected.

All Other Engines–400 hour intervals or earlier if valve sticking suspected until exhaust valve guides are replaced with guides made of improved material. (Refer to latest revision of Service Instruction No. 1485.)

Failure to comply with the provisions of this publication could result in engine failure due to excessive carbon build up between the valve guide and valve stem resulting in sticking valves or broken exhaust valves which result from excessive wear (bell-mouthing) of the exhaust valve guide.